SW6210503_Response To Comments_20211110

October 5, 2021
Jim Farkas
NCDEQ- Stormwater
512 N. Salisbury Street
Raleigh, NC 27699-1612
RE: Townsend Estates Subdivision
Jim;
We are re -submitting the plans for the Townsend Estates subdivision with the comments from the
September 28, 2021 review letter addressed. The comments are addressed as noted below:
1. Original Comment 3 —
The percent impervious
are for a drainage area is calculated as the total impervious area within the drainage
area divided by the drainage area. The Required Storm Volume calculation page
indicates that this value is 43.4% whereas Section IV, 10 indicates 24%. Please revise as
needed. There also appears to be a discrepancy between the BUA within the drainage
area to the proposed wet pond as shown in the Application/SCS Curve Number
calculation (347,022 sf) and the Supplement-EZ Form/Required Storm Volume
calculation (319,423 sf). Please ensure that the BUA shown within the drainage area to
the proposed wet pond is consistent.
a. I am sorry for the inconsistency; it should be handled now. I have carefully
reworked everything, and we should be on solid ground.
2. Original Comment 11— "...Please also ensure to include the cross-section at the
permanent pool elevation in the temporary storage stage -storage tables. "The
temporarypool stage -storage table was not updated to include the cross -sectional area
of the temporary pool at the permanent pool surface elevation (205.5 ft). The
previously provided calculations assume that cross -sectional area of the temporary
pool at the permanent pool elevation is zero sf based on the calculations (The
calculations show a cumulative storage between elevations 205.5 ft and 206.0 ft of
4,282 cf. The 4,282 cf volume divided by the 0.5 ft depth results in an average cross -
sectional area of 8,564 sf which is exactly half of the cross -sectional area at elevation
206.0 ft, which implies the surface area at elevation 205.5 ft is zero sf, which is
incorrect). Please revise as needed.
a. The calculations for the stage storage table have been modified such that the
incremental storage for the first data set (Elev. 206.0) is accurate.

3. Original Comment 13.b.i.1. — "The surface area of the proposed wet pond
does not need to be counted as impervious arei "The BUA calculations
indicate that the surfacearea of the permanent pool is 14,745 sf, however
this is less than the sum of the forebayand main pool surface areas at the
permanent pool elevation (2,961 sf and 12,244 sf respectively) as provided in
the revised stage -storage tables. Please revise as needed forconsistency.
a. 15,205 sf is the correct area of the pond NP that we are considering
impervious. Forms and computations have been updated to reflect
this.
4. Original Comment 13.b.ii.1. — "The entire site column should be an accounting
of the entire site, not just the drainage area to the proposed SCM. If there is
proposed BUA thatwill be constructed within the project area but will not drain
to the proposed SCM, it should be reflected in this column (in addition to the
on -site BUA within the SCM drainage area). The 'drainage area -for this column
is the project area and should matchthe information in the Application (as
1-d-' +" °' Q""' "The information in this column does not appear to be
correct. The plans indicate that there are 61 lots that are included in this
project. If each lot is allocated 4,100 sf of BUA, there should be a total of
250,100 sf of BUA located within the subdivided lots, however, Line 9 of the
Entire Site Column only shows 226,000 sf of BUA located within the subdivided
lots. Please ensure that all of the BUA that will be located within the project
area is accounted for in this column.
a. Corrected
Please clarify what the project area is for this project. Section IV, 7 and Line 5
of the Entire Site Column on the Drainage Areas Page of the Supplement-EZ
Form indicate thatthe project area is 27.20 ac, however Line 6 of the Entire
Site Column on the Drainage Areas Page of the Supplement-EZ Form indicate
that the on -site portion of the project area is 26.51 ac. Please revise or clarify
what this value is.
a. The site area got confused with the project area. Project area of 27.2
ac has been used everywhere.
6. Please clarify some discrepancies in the SCS Curve Number calculations page:
a. Using 56.5 lots at 4,100 sf per lot results in 231,650 sf of BUA
whereas 226,000sf is shown in the calculations.
b. This has been corrected to 54.5 lots within the DA and 6.5 lots
outside of the DA. The total lots in the prior calculation was not
409 Chicago Drive, Suite 112, Fayetteville, NC 28306
office 1910-426-6777 fax [phone]
On time, every time. I www.4Dsitesolutions.com

correct. All forms are updated.
c. As mentioned earlier, adding up the BUA within the drainage area on
this calculation page results in 347,022 sf of BUA which is different
than the amountshown in the Supplement-EZ Form and Required
Storm Volume calculation (319,423 sf).
d. All three agree with each other now.
e. The pre -development condition table indicates that there is 60,588 sf
of existing BUA within the drainage area to the proposed wet pond,
but the Supplement-EZ Form only shows 54,000 sf worth of existing
BUA.
f. 54,000 is correct and used for all the entries.
7. Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy
of other documents, and a response to comments letter briefly describing
how the comments havebeen addressed.
a. A new plan set has been uploaded although the only sheets that
changed were: C3.0, C5.3 & C6.1
b. PDFs must be uploaded using the format:
httl2s://edocs.deq.nc.gov/Forms/SW-Sul2l2lemental-UI21oad
c. Hard copies must be mailed or delivered to the following address:
i. For FedEx/UPS:
Suzanne McCoy
512 N. Salisbury Street,
Office 640K Raleigh, NC
27604
ii. For USPS:
Suzanne McCoy
1612 Mail Service Center
Raleigh, NC 27699-1612
Sincerely,
4D Site Solutions Inc.
Scott Brown, PE
[e-mail]
Enclosure
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